298 REAGENTS AND PROCESSES 



be taken not to breathe the fumes of the acid, since they attack 

 the mucous membranes. 



Diastase. — This may be prepared as follows: Germinate 

 barley in the incubator between pieces of blotting-paper until 

 the plumule has reached a length of about 2 mm.; then dry 

 the barley on the water-bath and grind to a fine powder. When 

 a diastatic solution is desired, pour over 10 gm. of the powdered 

 barley i liter of water containing 2 c.c. of chloroform; let stand 

 for ten hours at about 15° C. and filter. The water filtered off 

 will contain the diastase in solution. Add a little chloroform 

 and preserve in a dark place. Starch grains may be mounted 

 in this solution under a coverglass and kept from drying in 

 a moist incubator, and the effect of the diastase on the starch 

 may be studied from time to time under the microscope; or a 

 I per cent, starch paste may be made to which about an equal 

 amount of the diastatic solution may be added, and then at 

 intervals samples from the mixture of starch and diastase 

 may be tested with a solution of iodine. The starch will, 

 after a time, be changed into dextrines and grape-sugar and 

 will no longer give a blue color when tested with a solution of 

 iodine. 



Digestive Fluids. — To remove from sections aleurone grains 

 which are so numerous as to obscure the nucleus, the sections 

 should be treated for twenty-four hours with a digestive fluid 

 prepared by mixing i part of pepsin-glycerine with i part of 

 pancreatin-glycerine, and 20 parts of a 0.3 per cent, solution of 

 hydrochloric acid. Differences in the character of the proto- 

 plasmic cell-contents, and particularly in the dividing nucleus, 

 may be demonstrated by treating sections of fixed material with 

 a digestive fluid made by mixing i part of pepsin-glycerine with 

 3 parts of water acidified with 0.2 per cent, of chemically pure 

 hydrochloric acid. 



Diphenylamine. — This is a test for nitrates in plant tissues. 

 Five centigrams of diphenylamine are dissolved in 10 c.c. of pure 

 sulphuric acid. The presence of nitrates is to be assumed when 

 sections treated with this reagent take on a blue color. It 



